A sensor for detecting particles in an exhaust-gas stream is described in published German Patent Application DE 101 33 385. In the sensor described there, a collecting chamber is provided which can be coupled in fluid communication with an exhaust-gas stream of an internal combustion engine. A first electrode is situated on the upper side of the very flat collecting chamber, a second electrode on the lower side, thus opposite the first electrode. The collecting chamber between the two electrodes is hollow. When the known sensor is in operation, soot particles arrive in the collecting chamber and deposit in the hollow space between the two electrodes. The intervening space between the two electrodes is thereby electrically bridged, so that the impedance of the electrode structure changes. The change in impedance over time is a measure for the loading of the exhaust-gas stream with soot particles.
A sensor for detecting particles in an exhaust-gas stream is also described in published German Patent Application DE 101 33 384. There, the two electrodes are situated on the lower side of the collecting chamber and intermesh in comb-like fashion. The change in impedance between the two electrodes is a measure for the loading of the exhaust-gas stream with soot here, as well.
The sensor must be highly sensitive to precisely detect the loading of an exhaust-gas stream with soot. In this context, it holds true that the smaller the distance between the two electrodes, the more sensitive the sensor. In the case of the two known sensors described above, the distances between the two electrodes (“GAP”) are typically 30 to 100 μm. A further reduction in distances between the two electrodes is difficult from the standpoint of production engineering in the case of the known sensors, and can lead to durability problems during operation.
Therefore, an object of the present invention is to develop a sensor in such a way that it can be produced inexpensively, has a long service life, and at the same time, is able to detect the loading of a gas stream with particles with great accuracy.